Pickpockets who attend the avenues to public places to steal pocket-books, watches, &c. a superior kind of pickpockets. To knuckle to, to submit.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Knowledge Box * To Knuckle One’s WipeNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes